Should I switch to epoxy?

Mark42

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Am I beeing too stubborn insisting on using polyester resin instead of epoxy?

I have been pricing out the difference, and although the price is 2 to 3 times more for epoxy, I will probably only need about 2 gallons for the hard top project. That is about $110 epoxy (not West system brand) vs 50 for polyester.

But the biggest plus I see is I can use a much more rigid and surface coat free styrene foam instead of polyisocyanurate. One of the problems I had with polyisocyanruate that is available at the home centers is the paper face is darn hard to get off, and it's density is very low. The styrene foam is much higher density sands easy, stays rigid without a glass coating, and takes my simple impact test very well.

I have epoxy setting up on some styrofoam out in the garage right now. In a few hours, I give it the peel off test and see how well it holds onto styrene (it should, those sail boards I see are often made out of it).

I really would like to make the hard top out of foam. Switching to epoxy will let me do that.

I already bought and returned 4 sheets of polyisocyanurate foam to Home Depot, then bought the 1/4" ply. I have not cut into the 1/4" ply I bought Wednesday, so I can still return it and buy the pink rigid styrofoam.

My wife thinks I am losing it. :D
 

ondarvr

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Re: Should I switch to epoxy?

With the right foam either product will be strong and light, epoxy construction can be made lighter though. The problem is the grade of foam, even the best store bought foam won't be close to what's used in the marine industry, so it will be the weak link in the strucure. I'm not saying it "won't" work, it just would be much stronger with the right foam.
This means you will need to over build with glass to try and make up for the weak core.
 

Mark42

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Re: Should I switch to epoxy?

This means you will need to over build with glass to try and make up for the weak core.

Yep, thats the plan. The home store rigid styrine board is so much more denser and rigid than the polyisocyanurate boards, its like night and day.

I'm going to go buy some more styrine board and play with it before returning the ply.

The problem with experimenting is I end up changing direction so many times my head starts to swim. :)
 

Bondo

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Re: Should I switch to epoxy?

This means you will need to over build with glass to try and make up for the weak core.

Ayuh,........

If you're willing to go with more Glass,..............
The Strength of the core is not a big part of the equation Anyway.......

Glass,+ Resin alone will provide the Strength,.....
You just need the Foam to hold it In Place til it Sets.........
Covering All of the Foam creates a Structure that also creates Strength.......

Have you checked out Larry at raka.com,..??........ He's got some Real Reasonable pricing........
 

Mark42

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Re: Should I switch to epoxy?

I have calculated about 100 sq ft of surface to cover with glass/epoxy (total inside and outside).

Surf boards use a lightweight glass, 6oz or lighter because it drapes well. They also usually only apply two layers (from what I have read on surf board making websites).

I was going to use this same method, just use two layers of 6 oz, or maybe a 10oz layer covered with a 4 or 6 oz, then top coat, sand and paint. Do you think that amount of glass is sufficient?

All my glass work experience is from auto body and kit cars, and that was 20 years ago all done with heavy strand mat and poly resin. Kind of like wetting out a shag carpet. Then it was all covered with a thin layer of bondo. So I would appreciate hearing from folks who have layed up pieces like center console, live wells, etc from scratch.
 

Rob454

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Re: Should I switch to epoxy?

Ive used the honeycomb cardboard sheets with great success on fiberglass projects for customers. I used to build fiberglass enclosures ( boxes custom dock boxes, pretty much anythign that had to do with synthetic materials. I got into doing residential stuff but I got out of the busines the only problem youre gonna have with the pink foam is its not gonna suck in the resin. even the ridgid foam and it will also eventually delaminate if the part youre gonna make is a part that flexes a lot. Yo may want to get the thinnner sheets then place them on a 3/4 inch plywood sheet. coat one side with resin and fiberglass mat. then let it dry and do the other side.
Just a idea for you. the honeycomb cardboard is actually very very strong. I can stand on it and I barely put a impring on the surface and I weigh in at abotu 250 Lb. My buddy who is about 320 jsut puts a little deeper imprint.

Rob
 

Mark42

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Re: Should I switch to epoxy?

Rob, nothing better than someone posting their personal experience! Thanks for that great info.

When you say "honeycomb" cardboard, do you mean "corrugated" like the common cardboard box?


Thanks!

Mark
 

KnottyBuoyz

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Re: Should I switch to epoxy?

There's pleny of different types Mark. Dufaylite is one that comes to mind. I think Diab makes another. A quick google search will turn up plenty of links. Just remember what happens to cardboard when it gets wet! ;-)

I would think that total encapsulation is essential. I have seen my brother (cabinet maker) use it in doors and cabinet backs etc. He vacuum presses it in a veneer setup.
 

Mark42

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Re: Should I switch to epoxy?

I know from yesterdays tests on foam scrap that the epoxy does not soak in. To compensate, I plan on making small puncture marks (like that rolling meat tenderizer tool makes) or set the circular saw to about 1/8" and cut some cross score marks like diamond pattern.

When I pulled on the epoxy it would not come free of the foam, but it could be peeled from the edge, and a thin layer of foam comes off with it. So it does stick, the foam is just not nearly as strong as the epoxy.
 

Marcq

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Re: Should I switch to epoxy?

IMO, your best option is to make the surface of the foam as smooth as possible and coat it with mat and epoxy .A friend and I twenty years ago , build a F16 model aircraft (6' long) and the wings were made this way, I think we used only one coat, maybe two max, very strong, the plane actually crash twice without damaging the wings. Tough stuff

A foam cutter(hot wire) would do a good job chapping it the way you want it and it is easy to make and no sanding
Marc..
 

BillP

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Re: Should I switch to epoxy?

Assuming the hardtop won't be walked on or flex a lot the chance of delamination will be way less than if doing a normal deck. If you're following surfboard construction their foam is poured in a mold and the mold shut tight. The foam expands and the volume poured changes the density. Blanks are then cut lengthwise and wood stringers glued (and then clamped) in for strength with regular polyester resin. They tint or color the resin for cosmetics. Even a 1/8" softwood stringer increases strength dramatically. You could add stringers to any foam and glass over it.

In your case I'd use polyester and bulk up with more layers if needed. Also, you do NOT want open cell foam to suck very much resin up. It is sucking the resin OUT of the glass cloth and leaves a dry, brittle and weak glass job. The dryness is made from the 1000s of tiny pinhole size air bubbles between the cloth weave. This is a well known problem in the surfboard industry and the reason the resin is mixed to kick at the very minute the glasser finishs working the cloth.
 

Mark42

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Re: Should I switch to epoxy?

.... If you're following surfboard construction their foam is poured in a mold and the mold shut tight. The foam expands and the volume poured changes the density. Blanks are then cut lengthwise and wood stringers glued (and then clamped) in for strength with regular polyester resin. They tint or color the resin for cosmetics. Even a 1/8" softwood stringer increases strength dramatically. You could add stringers to any foam and glass over it.

...


That is good info, Bill, but I was reading websites that sell and mail foam blanks and they are nothing more than high density foam cut into rectangular blanks they mail you. No mold, no expansion, just foam that you lay epoxy over.

After forming the hard top from foam, I will then decide how many wood dowels to put through the foam to make a solid connection from inside to outside. I hope that is a good idea.

I stopped to look at a truck cap that was for sale on the side of the road today. It was a fiberglass top with plexy windows, and not very firm and only about 3/8" thick from what I could tell. Leaning on the top, it buckled, pushing on the sides, it moved easily. So that is what a single layer top is like, yet it gets very strong when bolted to the truck bed. Hopefully, my foam core top will be as strong as a truck cap when done.
 

fbnewbie

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Re: Should I switch to epoxy?

most of my research has shown to go with the 1/4'' ply and epoxy. There are some really good examples at www.fishyfish.com from all the Tolman skiff builders. Also, I believe that epoxy has a much harder time wetting out Mat than poly does, so you might want to consider cloth if you go with epoxy
 

Chris1956

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Re: Should I switch to epoxy?

Mark, Surfboard construction is very similar to what you are proposing. Surfboard blanks have a piece of wood down the center to give them added strength. Why not adopt this type of construction to add strength to your hardtop, with minimal increase in weight?

If you run a couple of wood strips (1x2s on end?) side to side, and fill between them with the foam, and glass the whole thing, the strength should increase dramatically.
 

pgdignan

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Re: Should I switch to epoxy?

I've used the epoxy over ply method on my boat (built from scratch) when used with cloth and a medium or slow hardener the wood bonds incredibly well to the fabric. I would think you'd be best off fully encapsuating a 1/4 piece of ply. Have you thought about using balsa core? they use it in alot of sailboat decking to keep the topside weight down and it's bendable.
 

BillP

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Re: Should I switch to epoxy?

That is good info, Bill, but I was reading websites that sell and mail foam blanks and they are nothing more than high density foam cut into rectangular blanks they mail you. No mold, no expansion, just foam that you lay epoxy over.

After forming the hard top from foam, I will then decide how many wood dowels to put through the foam to make a solid connection from inside to outside. I hope that is a good idea.

I stopped to look at a truck cap that was for sale on the side of the road today. It was a fiberglass top with plexy windows, and not very firm and only about 3/8" thick from what I could tell. Leaning on the top, it buckled, pushing on the sides, it moved easily. So that is what a single layer top is like, yet it gets very strong when bolted to the truck bed. Hopefully, my foam core top will be as strong as a truck cap when done.

If the blanks you are talking are high density they have already been blown in a mold and cut to whatever shape. If polyester resin eats them up they aren't polyurethane. The amount of liquid foam poured to make a surfboard blank would expand to near the size of an automobile if not put in a mold and expanded under pressure. That's how "high density" to get foam strength is done. It isn't something you make at home.

Walkerfoam dot com and Clarkfoam dot com are the two major surfboard blank mfgs here in the USA. Clark is typically higher density (stronger and heavier) than Walker. All these guys are pretty laid back dudes and might help you with a special project. I'd call and ask at least. They probably have a few surplus blanks laying around for cheap you could cut and glue up.
 

penst8grad

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Re: Should I switch to epoxy?

HAve you thought about building a frame with wood and using fleece as the support material instead of foam? That's how the car guys build subwoofer boxes.
 

seven up

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Re: Should I switch to epoxy?

Mark,

There's the pourable foam. Don't we know. Closed cell urethane. 2, 4 ,8, 16 lb densities. Soft flotation type 2 or rock hard 16. Once your mold is set and reinforced, walla, pour in the rest, trim, and your good to go. Pick your strength.

I'd go the 1/4" ply if building for myself, less complicated. Doubled or tripled for "stringers".

So what's up ?
 

kalla man

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Re: Should I switch to epoxy?

i think chris has the right idea here, wood stringers in the foam topped with a coupple layers of cloth would be plenty strong for a hardtop. (it would probably be fine with-out the stringers) I think i already brought my livewells to your attention mark. they are the R-max board with polly resin and 3 layers of 10oz. cloth, they bounce around at 50 mph full of water (about 7 gal.) I dont think your hard top with be under any stresses anywhere close to that.
Im excited about your project, cant wait to see results!
 
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